Hollow shapes are generally extruded using a porthole die. This specialized tool allows for the creation of profiles with internal cavities, like tubes or pipes.
Understanding the Porthole Die
To extrude hollow shapes, a porthole die is generally used. It is made up of two interlocking pieces — the mandrel and the cap. This design is crucial for forming both the external shape and the internal void simultaneously during the extrusion process.
Here's a breakdown of its key components and how they work together:
- The Mandrel: This part forms the internal features of the profile. It sits within the die and defines the shape and size of the hollow space.
- Portholes: The mandrel has multiple portholes separated by webs or legs for support. The material (e.g., aluminum alloy) passes through these portholes.
- The Cap: The cap forms the external shape of the profile and receives the material flow from the portholes.
- Welding Chamber: As the material exits the portholes, the streams recombine and weld back together in a chamber before passing over the mandrel and through the final die opening. This welding process is critical to ensure the integrity of the hollow shape.
The Extrusion Process with a Porthole Die
- Material Entry: Hot material (like an aluminum billet) is pushed into the extrusion press container towards the die.
- Flow Through Portholes: The material encounters the porthole die and is forced through the portholes, flowing around the supporting webs.
- Recombination & Welding: After passing through the portholes, the material streams meet again in the welding chamber behind the mandrel. Under the high pressure and temperature, these streams consolidate and weld together.
- Forming the Hollow Shape: The now welded material flows over the mandrel (which defines the inside diameter/shape) and through the outer die opening (defined by the cap, which defines the outside diameter/shape).
- Exiting the Die: The material exits the die as a continuous hollow profile (e.g., a tube, pipe, or other complex hollow section).
This innovative die design allows for the efficient manufacturing of a wide range of hollow profiles used in various industries, from construction and automotive to manufacturing and consumer goods.
